The power densities of modern, converter-fed three-phase drives are often the source of damage to roller bearings through spark or electro-corrosion. Such damage occurs, for example, when a high-frequency current with a high voltage gradient flows through the rolling elements and contact areas.

The electrical discharge causes the material to heat up and even melt at the surface. This can lead to considerable damage to the raceways, in the worst case complete failure of the bearing can occur. Visible signs for such damage are melting craters, particle break-out and discoloured lubricants.